There are numerous published articles reporting the differences in digestive processes of ruminant animals as compared with those of monogastric animals. Ruminant digestion is described in considerable detail, for example, by D. C. Church in "Digestive Physiology and Nutrition of Ruminants," Vol. 1, published by D. C. Church, produced and distributed by O.S.U. Book Stores, Inc., Corvallis, Oreg.
The ruminant animal lives on ingested forage consisting of large amounts of cellulose which it cannot digest directly. Instead of direct conversion of the forage, the ruminant animal has evolved a symbiotic relationship with microorganisms, consisting of a variety of bacteria and protozoa. The bacteria digest forage for their own survival and growth and the host ruminant animal later digests the microorganisms and their by-products.
Just as the ruminant animal requires certain preformed nutrients for its growth, the microorganisms upon which it depends for cellulose digestion have their own requirements for essential nutrients. M. P. Bryant and I. M. Robinson (J. Bacteriol. 1962, 84:605) studies the effect of certain compositions, including a mixture of acetic acid, isobutyric acid, valeric acid, isovaleric acid, and 2-methylbutyric acid on essential nutrition for the growth of ruminant microorganisms. Prominent among these microbes are the cellulolytic organisms upon which the ruminant depends. While it has also been shown by others that not all of these volatile fatty acids are required by all of the organisms, at least one is required by each of the 23 for which the combination was shown to provide essential nutrients and each one was essential for at least one of these same 23.
Volatile fatty acids have been shown to be incorporated into the structure of these microorganisms by conversion to characteristic lipids and amino acids, such as ethanolamine plasmalogen, valine, and isoleucine.
These acids are normally present in the rumen as a result of catabolism by the microorganisms of amino acids derived from the protein in the diet of the ruminant animal. Diets high in good quality protein may contain a sufficient supply of CCN precursors for optimal growth of cellulolytic organisms on such diets. However, high-protein diets are expensive and utilize either feedstuffs alternatively convertible to use directly by man or feedstuffs grown on land suitable for the growth of human food crops. It would be desirable to reduce the amount of expensive good quality protein in ruminant feeds and still be able to efficiently utilize cellulose, a foodstuff not utilizable directly by man.
Ruminant nutritionists have shown that during the digestive process, in the rumen of cattle, bacteria break down feed protein to ammonia and fatty acids. The bacteria then use the ammonia to synthesize cellular protein. These bacteria pass from the rumen to the abomasum and the intestine where they are digested and serve as the major source of protein for maintenance of body tissues and for milk production. Extensive studies on the nutrition of rumen bacteria have shown that fiber-digesting bacteria require certain isoacids, such as isobutyric acid, as well as ammonia for synthesis of bacterial protein. (Dairy Notes, November, 1973, p. 7, Dr. Robert M. Cook, Michigan State University published by the Cooperative Extension Service.) Without isoacids, urea or NH.sub.3 cannot be utilized by these rumen bacteria. For many years cattle rations have been supplemented with non-protein-nitrogen (NPN) in the form of urea or ammonia.
Patents of interest include U.S. Pat. No. 3,564,098 which discloses a method of improving growth response in ruminants which comprises orally administering certain acids, including valeric acid. Also, U.S. Pat. No. 3,982,028 discloses that volatile fatty acids are absorbed through the rumen walls and are utilized by the animal as primary energy sources. The effects of isoacids (isobutyric, isovaleric, 2-methylbutyric and valeric on milk production were reported in 1980 J. Dairy Sci. 63:1098-1103.